Config is a fluent builder. It is immutable after open(), and a subset of its values become the durable identity of the database, persisted in the IDENTITY file.

Identity (frozen at first open)

Three values are durable: dimension, metric, and index type. Reopening with a conflicting value raises ConfigError.

python

db = elips.open(
    "/var/lib/myapp/elips",
    dimension=384,
    metric="cosine",       # "cosine" | "euclidean" | "dot"
    index="graph",         # "graph" (HNSW) | "exact"
)

Indexes

graph is the default — a Hierarchical Navigable Small World graph backed by HierarchicalGraphIndex. exact performs a brute-force scan and is suitable for small vaults, test workloads, and ground-truth measurement. Both implement the same IndexPort contract; see Algorithms.

cpp

auto db = elips::open(
    "/tmp/elips",
    elips::Config{}
        .dimension(128)
        .metric(elips::Metric::cosine)
        .graph_params({.M = 16, .ef_construction = 200, .ef_search = 64}));

Durability

Mode	Behaviour
`paranoid`	Flush and `fsync` on every WAL append.
`standard`	Flush on every append.
`relaxed`	Buffer; flush at checkpoint and close.
`ephemeral`	No WAL is attached. In-memory only.

Persistence

Segmented storage is on by default. Disable it with Config::segmented_storage(false) to fall back to the single-file elips.snapshot format. Both formats are crash-safe; Storage & recovery walks the on-disk layout.

Embedders

New databases auto-attach the built-in local text embedder. Two explicit choices are supported:

Config.local_text_embedder(...) — a rehydratable local embedder. ELIPS restores it automatically on reopen via TEXT_EMBEDDER.manifest and a deterministic artifact.
Config.text_embedder(callable, ...) — a Python callable. Metadata is persisted, but reopening without providing the same callable causes text-first APIs to raise ConfigError rather than silently degrading.

Access mode

read_write takes an exclusive advisory lock — one writer per database. read_only takes a shared lock and rejects every mutation path with StorageError. Use read-only mode for shared-reader analytics or fan-out serving.

python

reader = elips.open("/var/lib/myapp/elips", access_mode="read_only")
print(reader.vault("documents").seek_text("alpha", top=1)[0].data)